Behçet's syndrome (BS) is a disease of unknown etiology, and as such, there have been efforts to classify BS within the popular nosological identities of the times such as seronegative spondarthritides, autoimmune, and more recently autoinflammatory diseases. Current evidence suggests that BS does not easily fit into any one of these lumps, while on occasion, it might be impossible to tell BS from Crohn's disease, especially when the main clinical presentation is intestinal ulceration. There are distinct regional differences in disease expression of BS with fewer cases of intestinal disease in the Mediterranean basin and less severe eye disease and less frequent skin pathergy among patients reported from northern Europe or America. The clustering of symptoms, especially with the recently described increased frequency of the acne/arthritis cluster in familial cases, suggests that more than one pathological pathway is involved in what we call BS today. Supportive evidence for this contention also comes from the observations that (a) the genetic component is very complex with perhaps different genetic modes of inheritance in the adult and in the pediatric patients; and (b) there are differing organ responses to one same drug. For example, the anti-TNF agents successfully control the oral ulcers while they have no effect on the pathergy reaction. © Springer Science+Business Media, LLC 2012.